Extracellular and intracellular pathogen recognition by members of the TLR and NLR families initiate innate immune and inflammatory responses. TLRs and NLRs both activate the NF-?B and MAPK signaling pathways leading to the transcription and secretion of multiple inflammatory cytokines (e.g. TNF1, IL-6, and IL-8). Unlike TLRs, NLRs can also activate multiprotein inflammasome complexes that processes proIL-12 and proIL-18 to their active forms. In less than five years, NLRs have been linked to hereditary autoinflammatory diseases and innate immune response towards a growing number of pathogens, including Bacillus anthracis, Yersinia pestis, and Francisella tularensis. Inflammasome assembly results from interaction of a pyrin containing NLR protein with ASC (apoptotic speck protein with a CARD) followed by recruitment and activation of Caspase-1. The inflammasome complex may also be involved in inducing a form of caspase-1 dependent apoptosis. ASC interactions with NLRs and the protein Pyrin can also activate NF-?B. Recently, the discovery of pyrin only proteins (POPs) that influence both NF-?B and inflammasome functions has suggested an avenue for host regulation of the proinflammatory response and pathogen subversion thereof. The long-term objective of this proposal is to understand the molecular regulation of innate immune responses dependent upon pyrin only proteins. Further, understanding of inflammasome regulation will be extended to host-pathogen interactions where inflammasome function or subversion is demonstrated to be critical for immunity or disease. Specifically, we have identified a second human POP (POP2) which inhibits NF-?B p65 activity, interacts with ASC, and prevents the activation of a number of NLR activated inflammasomes. We will test the hypothesis that POP2 negatively regulates proinflammatory responses by interfering with both inflammasome-mediated caspase-1 activation and attenuating NF-?B signals, thus dampening harmful inflammation and preventing or reducing macrophage death during innate immune responses. Combining broad based molecular and in vivo approaches, we will address the following aims: 1) Establish the molecular basis for NF-?B inhibition by POP2 2) Establish the molecular basis for POP2 regulation of inflammasome activation. 3) Establish the in vivo role of POP2 in modulating inflammatory innate immune responses. PUBLIC HEALTH RELEVANCE: Inflammatory responses resulting from injury or infection are a significant threat to human health. We propose to study a small protein called POP2 which is expressed in inflammatory cells and can regulate cellular events leading to inflammation. This study is therefore relevant to a wide range of inflammatory diseases and conditions, ranging from infection to cardiovascular disease.